Magnetic Tape Facilities



DMAGCLAIM

%externalintegerfn DMAG CLAIM(%string(6)TSN, %integername SNO,
      %integer REQ, MODE)

 The magnetic tape volume labelled TSN is either claimed (REQ=0) or
 released (REQ=1).  MODE should be set to 1 to allow read access to the
 tape, 2 if write access is required, or 3 for either read or write
 access.   If a CLAIM call is successful, SNO is set with a number to be
 used in subsequent calls of DMAG IO.

 If TSN is null in a RELEASE call, then all claimed tapes are released.

 Possible error results from Volumes:
           101  Bad parameters
           102  Duplicate request
           103  Request lists full
           104  Volume not available (Operators have said "NO <val id>")
           105  Volume request list full
           106  No tapes in tape list (A, B, S or E)
           107  Device not claimed when a "release" is done.


DMAGIO

%externalintegerfn DMAG IO(%integername REPLY FLAG, CONTROL, LEN,
      %integer TYPE, SNO, ADR)

 The parameter TYPE determines the action of the procedure:
   TYPE = 0 erase
          1 read
          2 write
          3 check-write (not implemented)
          4 check-read (no data transfer)
          5 private chain (not implemented)
          6 rewind to BT
          7 spare
          8 file position
          9 tape position
         10 write tape-mark

 SNO should be set with the value returned by a previous CLAIM
 (procedure DMAG CLAIM).  ADR and LEN specify the area from or to which
 data is to be transferred (if relevant).  In the case of TYPE = 1
 (read) LEN is set on return to be the number of bytes transferred.

 Bits in parameter CONTROL are used to specify detailed actions by the
 tape handler routine, as follows:

        2**0  -
        2**1  suppress error re-try
        2**2  ignore short-block indication
        2**3  ignore long-block indication

 Bits in CONTROL on return are used to indicate the occurrence of
 conditions during execution of a request, as follows:

        2**0  short-block indication
        2**1  long-block indication

 These bits will not be set on return if the respective bits for
 "ignore short/long-block indication" were specified in the request.
 REPLY FLAG (valid when the result of the function is zero) is set
 to zero for a successful operation, or

        1   failure (parity etc.)
        2   request rejected
        4   beginning of tape, end of tape or unexpected tape
            mark found, but operation otherwise successful


 TYPE=8

 For request TYPE=8 (file position), LEN specifies the number of blocks
 to be skipped: negative means backwards, positive forwards, zero is
 invalid. If a tape-mark is found (REPLY FLAG=4) then a skip back of one
 block is performed before the reply is given.  It is thus impossible
 to pass a tape-mark except by the use of a "tape position" request.

 TYPE=9
 For request TYPE=9 (tape position), LEN is the number of (notional)
 files to be skipped, and CONTROL is the number of tape-marks in a
 notional file, CONTROL must be positive.  If LEN is negative the skip
 is backwards, if positive then it is forwards, zero is invalid.
 CONTROL*LEN tape-marks are skipped.  A backwards skip will stop at BT.
 A forward skip will stop if the first block within a (notional) file is
 a tape-mark, the tape will then be positioned before the tape-mark and
 REPLY FLAG=4 will be returned.  Thus if CONTROL=1 and LEN="very large",
 the tape will be positioned between the first double tape-mark
 encountered.